I did switch Step 2 and Step 3 and tested "flatten-first, then sign". It worked. However, this way, the flatten output gave me two pages instead of one - the source pdf has only one page. Among the two pages, the first page is what I wanted, but the second one is a blank form which is exactly same as the first page. Where does this blank page come from? Was there something wrong when I generated the PDF form in LC Designer? I did nothing but using the default template - Conference Registration!

Please help. The original PDF form and the flatten output file are attached.